The interaction of small particles suspended in air with the ions normally produced in the air is discussed. The neutralization of highly charged dust particles, if suspended in air, is treated in detail. The result is found to be in qualitative agreement with experiment. The special case of final equilibrium is investigated. It is found that multiply charged particles should be present in appreciable number in coarse aerosols at all times. This is confirmed by experiments both for initially charged quartz dust and for initially neutral ammonium chloride smoke. The general nature of an equilibrium charge distribution is presented. Charges up to ten electron units are found to be not uncommon.